Field of the Invention
The present invention relates to a rotation angle detection sensor that utilizes a Hall element.
Description of Related Art
Japanese Patent No. 4936299 has disclosed a magnetic field direction detection sensor in which a disc-shaped magnet is coaxially fixed to an axial end of a rotary shaft. The magnet is magnetized along one diameter line thereof. An N-pole is generated at an edge of the magnet along one of semicircles thereof, and an S-pole is generated at an edge of the magnet along the remaining semicircle thereof. A magnetic field is formed based on these N-pole and S-pole. When the rotary shaft rotates, the magnetic field rotates around an axis of the rotary shaft.
A plurality of Hall elements are faced to a surface of the magnet. Each of the Hall elements outputs an electric signal in accordance with a direction and a magnitude of magnetic force lines. The Hall elements are arranged, for example at equal intervals, around a line extended from the axis, and for each diameter line, outputs of two Hall elements are differentially amplified. For detecting a rotation angle (angle position), two output signals having a phase difference therebetween are generated.
In Japanese Patent No. 4936299, the disc-shaped magnet is positioned coaxially with the axis of the rotary shaft. Moreover, the arrangement including the plurality of Hall elements is also positioned coaxially with the axis of the rotary shaft. When a differential amplification signal is disturbed due to positional deviation or unevenness in magnetization, it is difficult to specify the rotation angle.
Japanese Patent Application Laid-open No. 2014-141251 has disclosed one Hall element arranged radially outward of a disc-shaped magnet. Since a shift lever rotates only in a narrow angle range, a rotation angle can be specified by the one Hall element. However, when the angle range is widened, an output of the Hall element and the rotation angle cannot correspond to each other one-on-one, and a transducer device in Japanese Patent Application Laid-open No. 2014-141251 cannot specify the rotation angle. Further, since the magnet has an outer peripheral surface formed as a cylindrical surface that is uniform over its whole periphery, it is not possible to specify a magnetization direction, and therefore it is difficult to arrange the Hall element in a predetermined attitude with respect to the magnetization direction.